When Clement Rodney Hampton-el, a hospital technician from Brooklyn, New Jersey, returned home from the war in Afghanistan in 1989, he told friends his only desire was to return. Though he had been wounded in the arm and leg by a Russian shell, he said he had failed. He had not achieved martyrdom in the name of Islam.

So he found a different theatre for his holy war and achieved a different sort of martyrdom. Three years ago, he was convicted of planning a series of massive explosions in Manhattan and sentenced to 35 years in prison.

Hampton-el was described by prosecutors as a skilled bomb-maker. It was hardly surprising. In Afghanistan he fought with the Hezb-i-Islami group of mujahideen, whose training and weaponry were mainly supplied by the CIA.

He was not alone. American officials estimate that, from 1985 to 1992, 12,500 foreigners were trained in bomb-making, sabotage and urban guerrilla warfare in Afghan camps the CIA helped to set up.

Since the fall of the Soviet puppet government in 1992, another 2,500 are believed to have passed through the camps. They are now run by an assortment of Islamic extremists, including Osama bin Laden, the world's most wanted terrorist.

Bin Laden arrived in Afghanistan from Saudi Arabia in 1979, aged 22. Though he saw a considerable amount of combat - around the eastern city of Jalalabad in March 1989 and, earlier, around the border town of Khost - his speciality was logistics.

From his base in the Pakistani city of Peshawar, he used his experience of the construction trade, and his money, to build a series of bases where the mujahideen could be trained by their Pakistani, American and, if some recent press reports are to be believed, British advisers.

One of the camps bin Laden built, known as Al-Badr, was the target of the American missile strikes against him last summer. Now it is used by Harkat-ul-Mujahideen, a Pakistan-based organisation that trains volunteers to fight in Kashmir.

Some of their recruits kidnapped and almost certainly killed a group of Western hostages a few years ago. The bases are still full of new volunteers, many

Pakistanis. Most of those who were killed in last August's

strikes were Pakistani.

A Harkut-ul-Mujahideen official said last week that it had Germans and Britons fighting for the cause, as well as Egyptians, Palestinians and Saudis. Muslims from the West as well as from the Middle East and North Africa are regularly stopped by Pakistani police on the road up the Khyber Pass heading for the camps. Hundreds get through. Afghan veterans have now joined bin Laden's al-Qaeda group.

Some have returned to former battlegrounds, like the university-educated Dr Ayman al-Zawahiri, a key figure in the Egyptian al-Jihad terrorist group. Al-Zawahiri ran his own operation during the Afghan war, bringing in and training volunteers from the Middle East. Some of the $500 million the CIA poured into Afghanistan reached his group. Al-Zawahiri has become a close aide of bin Laden and has now returned to Afghanistan to work with him. His al-Jihad group has been linked to the Yemeni kidnappers.

One Saudi journalist who interviewed bin Laden in 1989 remembers three of his close associates going under the names of Abu Mohammed, Abu Hafz and Abu Ahmed. All three fought with bin Laden in the early Eighties, travelled with him to the Sudan and have come back to Afghanistan. Afghan veterans, believed to include men who fought the Americans in Somalia, have also returned.

Other members of al-Quaeda remain overseas. Afghan veterans now linked to bin Laden have been traced by investigators to Pakistan, East Africa, Albania, Chechnya, Algeria, France, the US and Britain.

At least one of the kidnappers in Yemen was reported to have fought in Afghanistan and to be linked to al-Quaeda. Despite reports that bin Laden was effectively funded by the Americans, it is impossible to gauge how much American aid he received. He was not a major figure in the Afghan war. Most American weapons, including Stinger anti-aircraft missiles, were channelled by the Pakistanis to the Hezb-i-Islami faction of the mujahideen led by Gulbuddin Hekmatyar.

Bin Laden was only loosely connected with the group, serving under another Hezb-i-Islami commander known as Engineer Machmud. However, bin Laden's Office of Services, set up to recruit overseas for the war, received some US cash.

But according to one American official, concentrating on bin Laden is a mistake. 'The point is not the individuals,' he said last week. 'The point is that we created a whole cadre of trained and motivated people who turned against us. It's a classic Frankenstein's monster situation.'

Others point out that the military contribution of the 'Arabs', as the overseas volunteers were known, was relatively small. 'The fighting was done by the Afghans and most of them went back to their fields when Kabul fell to the mujahideen,' said Kamaal Khan, a Pakistani defence analyst. 'Ironically, the bulk of American aid went to the least effective fighters, who turned most strongly to bite the hand that fed them.'